Journal of Lipid Research, Vol 22, 485-495, Copyright © 1981 by Lipid Research, Inc.
Origins of fecal neutral steroids in rats
TA Miettinen, A Proia and DJ McNamara
The origins of rat fecal neutral steroids were studied in male and female
animals fed a sterol-free diet and maintained in an isotopic steady state.
The specific activity of fecal cholesterol was found to be consistently
lower than that of plasma cholesterol and of the fecal bile acids,
indicating that a considerable portion of the fecal neutral steroids was
derived from cholesterol not in equilibrium with the rapidly exchangeable
pool of body cholesterol. This non-exchanging fraction of neutral steroids
was larger in male than in female rats; it appeared to have at least two
origins: skin surface lipids licked off fur, and sterols newly synthesized
by the intestinal mucosa and secreted into the gut lumen. When the
ingestion of skin sterols rich in cholesterol precursors was minimized, the
proportion of the non- exchanging fraction of fecal neutral sterols fell
somewhat, but the output of cholesterol precursors dropped markedly. This
suggests that a significant portion of the non-exchanging fecal cholesterol
fraction originated in the intestinal wall by secretion. It can be
concluded that the fecal neutral steroids of rats originate primarily from
three sources: 1) de novo cholesterol synthesis by the intestinal mucosa,
2) ingested dietary, skin, and fecal sterols, and 3) a rapidly exchangeable
cholesterol pool excreted through bile, the intestinal wall, or both.